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    Re: star-to-star distances
    From: Bill Noyce
    Date: 2004 Sep 30, 15:11 -0400

    Alexandre Eremenko wrote:
    > This can be easily fixed, of course, just by
    > tabulating ALL mutual distances between the usual 57 navigational
    stars.
    
    Be careful -- the stars' apparent positions, even after correcting for
    refraction, vary over the course of a year by several tenths of a
    minute.
    This is called "annual aberration" or "aberration of starlight" or
    "stellar aberration", and is caused by changes in the direction of
    earth's
    orbital motion.  A star's apparent position shifts by an amount equal to
      arctan ( orbital_speed / speed_of_light )
    toward the direction of the earth's motion.
    
    Historical note -- this effect was first discovered by astronomers
    who were trying to measure parallax of stars (using the earth's orbit
    as a baseline) to determine how far away they are.  It turns out that
    parallax is (almost always?) a much smaller effect.
    
    
    

       
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